318 Professor E. B. Poulton on colour -relation 



it always responds in this way to an environment of the 

 kind described above. Bidentata doubtless occupies an 

 intermediate position between the other two species in 

 this respect. The occasions are probably rare, but not 

 altogether wanting, in which it is compelled to develop in 

 a green environment. We find that it has the power of 

 making some considerable approach towards such surround- 

 ings, but not of attaining any liigh degree of resemblance to 

 them. It is probably the case^ however, that the tint which 

 it produces on green leaves and shoots is of great value 

 on a pale yellowish-brown bark, which may often form its 

 enviromnent ; and it may well be that it is something 

 in common between the light reflected from this and from 

 green leaves which explains the similarity in the effects 

 produced upon the larvse. 



Typical examples of all the forms of qucrnifolia larvoe 

 produced in these experiments wei'e shown alive at the 

 meeting of the Entomological Society of London on May 

 2nd, 1894, and also at the Soiree of the Royal Society in 

 the same month. A brief account of the exhibit is printed 

 in the Proc. Ent. Soc. Lond., 1894, p. xvi. It is also referred 

 to in Mr. C. G. Barrett's " Lepidoptera of the British 

 Islands" (Lond., 1896, vol. iii, p. 45). 



The nearly mature larvae of quercifolia, forming the 

 subject of the experiments described in this memoir, were 

 in almost every case sent to Lord Walsingham, and, with 

 the exception of one which was spoilt, were kindly preserved 

 by him. The specimens are now to be seen in the Hope 

 Department, Oxford University Museum, and in the British 

 Museum of Natural History. 



The last series of experiments described in this paper 

 grew out of the surprising restriction of susceptibility to 

 the younger stages of G. quercifolia. The results naturally 

 suggested further experiments upon other species well 

 known to be highly sensitive, and I immediately fixed 

 upon Am/pliidasis betnlaria as the most suitable for the 

 purpose. The investigation was carried out entirely by 

 the present writer, in the laboratory at Wykeham House, 

 Oxford. The results are clearly shown in the accompany- 

 ing diagram and summary. The Roman figures represent 

 the corresponding stages of larval life. The shaded squares 

 indicate stages passed in a black environment, the unshaded, 

 stages passed in the green surroundings. 



